Numerical control apparatuses which control a multiplicity of axes or spindles are widely used to effect machining at a high speed. This type of the numerical control apparatus contains a plurality of microprocessors (CPUs), and the axes to be controlled are assigned to each CPU, respectively. More specifically, each CPU has an independent axis arrangement, and therefore, the axes to be controlled by each CPU are prefixed, and the axes which can be interpolated by each CPU are fixed by the axis arrangement thereof.
The prior art will be described below with reference to the drawings, wherein FIG. 4 shows a prior art axis control system for a numerical control apparatus.
A CPU 11 controls an axis arrangement composed of an axis X1 an axis Y1, a Z-axis, and a C-axis; a CPU 21 controls an axis arrangement composed of an axis X2 and an axis Y2; ROMs 12 and 22 are composed of an EPROM or an EEPROM and store the system program of the CPUs 11 and 21; and RAMs 13 and 23 are composed of a SRAM or the like and store various data or input/output signals. Although not shown, a non-volatile memory supplied with power from a battery, a graphic control circuit, a display, an operator's panel and the like are connected to the CPUs 11 and 21, through a bus, in addition to the above-described units.
Each axis is composed of a position control circuit, a servo amplifier, and a servo motor, and since the respective axes have the same arrangement, only the axis X1 will be described here.
A position control circuit 14a receives a position command from the CPU 11 and outputs a speed command signal to a servo amplifier 15a for controlling a servo motor 16a. The servo amplifier 15a amplifies the speed command signal and drives the servo motor 16a.
Although not shown, a position sensor for outputting a position feedback signal and a tachometer generator for outputting a speed feedback signal are connected to the servo motor 16a, respectively. A pulse coder or the like is used as the position sensor to feed back a position feedback pulse to the position control circuit 14a. The tachometer generator feeds back a voltage signal in accordance with a rotational speed of the servo motor 16a to the servo amplifier 15a.
Interpolation signal generation circuits 17 and 27 count a system clock supplied thereto and output an ITP (interpolation) cycle signal at a predetermined timing. The ITP (interpolation) signal output is usually made at intervals of 8 milliseconds. The CPUs 11 and 21 manage an interpolation processing time in response to the interpolation cycle signal.
The CPU 11 is connected to the CPU 21 through a bus, and data is exchanged therebetween through the bus.
In the prior art axis control system, since the ITP (interpolation) cycle signal serving as an interpolation criterion is created by the respective different interpolation signal generation circuits 17 and 27, the CPUs 11 and 21 generate the interpolation cycle signal at a different timing. As a result, a problem arises in that the CPU 11 can control the axis X1, the axis Y1, the Z-axis, and the C-axis, but cannot control the axis X2 and the axis Y2, whereas the CPU 21 can control the axis X2 and the axis Y2, but cannot control the axis X1, the axis Y1, the Z-axis, and the C-axis.